#define  _CRT_SECURE_NO_WARNINGS  1
#include <stdio.h>
int main()
{
	int scores = 0;
	scanf("%d", &scores);
	char x;
	if (scores >= 90 && scores <= 100)
	{
		x = 'A';
	}
	else if (scores >= 80 && scores < 90)
	{
		x = 'B';
	}
	else if (scores >= 70 && scores < 80)
	{
		x = 'C';
	}
	else if (scores >= 60 && scores < 70)
	{
		x = 'D';
	}
	else if(scores >= 0 && scores < 60)
	{
		x = 'E';
	}
	else
	{
		x = 'F';
	}
	printf("%c", x);

	return 0;
}